I'd like to make vfio-pci capable of manipulating the device exposed to the user such that if the host can only support a single MSI vector then we hide the fact that the device itself may actually be able to support more. When we virtualize PCI config space and interrupt setup there's no PCI protocol for the device failing to allocate the number of vectors that it said were available. If the userspace driver is a guest operating system, it certainly doesn't expect this to fail. I don't think we can ever guarantee that a multi-vector request will succeed, but we can certainly guarantee that it will fail if the platform doesn't support it. An example device is the Atheros AR93xxx running in a Windows 7 VM. Both the device and the guest OS support multiple MSI vectors. With interrupt remapping, such that the host supports multivector, the device works well in the guest. With interrupt remapping disabled, the device is far less reliable because of the mismatch in MSI programming vs driver configuration and often fails. If vfio-pci can test whether multiple vectors are supported, then we can make it work reliably in both cases by adjusting the exposed MSI capability, like in this patch that would follow this series: https://github.com/awilliam/linux-vfio/commit/9ace67515680 With this series, only x86 w/ interrupt remapping will advertise support for multiple MSI vectors. In surveying the code, I couldn't find any other archs that allowed it, but I'll take corrections if that's untrue. Thanks, Alex --- Alex Williamson (3): PCI: Extend and export pci_msi_supported() for multivector MSI PCI/x86: Add arch_supports_multivector_msi() hook PCI/MSI: Initial hook for archs to declare multivector MSI support arch/x86/include/asm/x86_init.h | 1 + arch/x86/kernel/x86_init.c | 6 ++++++ drivers/iommu/irq_remapping.c | 6 ++++++ drivers/pci/msi.c | 20 +++++++++++++++++--- include/linux/msi.h | 1 + include/linux/pci.h | 3 +++ 6 files changed, 34 insertions(+), 3 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
